1. Field of the Invention
This invention relates to the field of radio frequency (RF) tagging. More specifically, the invention relates to an improved method for creating an RF antenna on a lightweight, flexible substrate through demetallization of the substrate around the antenna pattern, leaving the metallized antenna.
2. Background of the Invention
Radio frequency (RF) tagging or identification is one of many technologies for identifying and/or tracking objects. The RF identification process requires that information be carried on a substrate such as a tag or label containing an antenna. The antenna allows reception and transmission of radio waves. Typically, the tag or label containing the antenna reflects an incident RF carrier back to a base station. It radiates or receives energy and can be structured to radiate or receive energy over varying bandwidths.
The tag usually consists of a semiconductor chip containing RF circuits, logic and memory and it also contains an antenna, the formation of which is the subject of this invention.
A number of methods of manufacture of RF antennas are well known in the field. The principal known techniques for fabricating RF antennas include foil forming, dip brazing and electroforming of metallic-based structures. The antennas are generally loops of wire soldered to a circuit card or consist of metal etched or plated on a circuit card. Much of the prior art has produced thick, stacked and layered tags with components mounted on cards and covered in plastic, resulting in a rigid package. None of the known systems provides for production of antennas of varying densities.
More recent inventions have reduced both the cost and weight of an RF antenna by creating antennas on thin flexible tags, Such a process is described in U.S. Pat. No. 5,528,222. This method embeds metal into the substrate that forms the tag, which requires a high density deposit of metal. The tag or label containing the antenna must then be laminated to an additional substrate, resulting in a thickness of up to 50 micrometers. Such a thickness creates a less flexible tag or label and restricts its range of applications.
Another formation method is described in U.S. Pat. No. 4,220,956, in which the antenna array is created by etching a copper laminate that is adhered to one side of a thin substrate. The structure described claims a total thickness of less than 0.005 inch, which can be manufactured as a thin flexible, rollable, lightweight array. The antenna is created using an etching process substantially the same as that used for forming printed circuit boards and microstrip antennas. In this process, the resulting thickness still reduces the flexibility and applicability of the tag or label.
None of these methods provides an approach to the design and fabrication of RF antennas that reduces cost, thickness, and weight of the antenna tag or label that also increases its flexibility to allow for a virtually unlimited number of applications.